The present invention relates to a pattern forming method which can be used in manufacture of semiconductor elements, printing plates etc., and particularly relates to a pattern forming method for selectively forming a film on an arbitrary substrate by use of chemical reactions.
Heretofore, resist patterns in the manufacture of semiconductor elements or resin patterns which provide negative plates in the manufacture of printing plates have been manufactured in the following manner: A resin film which may be polymerized or decomposed by irradiation of light is formed on the substrate and, then, light beams are irradiated in any arbitrary pattern on the resin film, followed by development, thereby forming the pattern. More and more refining of these resist patterns has become demanded for attainment of higher density of semiconductor elements and higher quality of printed forms.
Particularly, in the manufacture of very large scale integrated circuit (VLSI), there has arisen the need for forming at a high accuracy a resist pattern in fine lines of submicron order. While this process is largely affected by the physical properties of the resist itself, generally, the finer the pattern it is desired to have (thus, for increasing the resolution), the resist film applied needs to thinner. On the other hand, when it comes down to providing submicron patterns, wet etching can not be utilized, but such a dry etching as ion etching, plasma etching or sputter etching, etc., must be utilized. In order to improve the dry etching resistance of the resist pattern, generally, the resist coating needs to be thick.
Accordingly, in order to meet the above-stated two requirements, it is advisable to develop a photoresist whose coating is thick, but gives high resolution, or a photoresist whose coating is thin but gives high dry-etching resistance. However, presently, there is available no such material.
On the other hand, heretofore, resist patterns used in manufacturing integrated circuits (IC) are generally formed in the following manner: The photoresist is applied on a semiconductor substrate by use of a rotary coating device using a spinner and the substrate is exposed in a specified pattern, followed by development, thereby forming the resist pattern. Recently, to fill the need of fine pattern forming in manufacturing VLSI, forming a resist pattern which is highly accurate in pattern dimensions and which moreover, has no pin-hole is desired. However, generally, when the method of applying the photoresist by the rotary coating is used, if the semiconductor substrate which forms the base has any stepped parts, the film thickness of the photoresist becomes irregular, thus the coating being thinner at the top of each convex part, but thicker at the bottom of each concave part. Therefore, even if the exposure is made with a photo-mask having an equal line width, the line widths of the pattern differ between that at the top of the convex part and that at the bottom of the concave part. Furthermore, to achieve the pattern of the order of 0.5-1 .mu.m at a high accuracy as in manufacturing VLSI, the thickness of the photoresist coating needs to be reduced. However, taking account of etching resistance and prevention of pin-hole when applying the coating, the film thickness needs to be larger than a certain value and due to this coating thickness, there is a limitation in the forming of the fine pattern.
Further, as a method of forming thin film having no pin-hole, a forming method of very thin photoresist film using the Langmuir Blodgett's technique (hereinafter referred to as LB technique) is in the process of development. However, by this method, the pattern can be obtained at a high accuracy, but since the coat thickness of one layer is on the order of 20-30 .ANG., normally about 100 layers need to be formed in order to resist the plasma etching in manufacturing IC.